1. Field of the Invention
The present invention relates to a nitride semiconductor thin film having fewer defects and a method of growing the same. More particularly, the present invention relates to a nitride semiconductor thin film having fewer defects and a method of growing the same wherein a nitride semiconductor thin film having lower defect density can be obtained by forming grooves on a substrate, sequentially forming a buffer layer and a first nitride semiconductor thin film on an entire top surface of the substrate, etching higher defect density regions of the first nitride semiconductor thin film, and then laterally growing a second nitride semiconductor thin film.
2. Description of the Related Art
In general, nitride semiconductor thin films are widely used in optical devices capable of emitting light in a short wavelength region using a wide band gap, and research on the applications of high-temperature, high-frequency and high-power electronic devices have been actively performed.
These nitride semiconductor thin films are grown on a sapphire substrate that is generally stable at high temperatures.
However, since there are significant differences in the coefficient of thermal expansion and lattice constant between the nitride semiconductor thin film and the sapphire substrate, there is a problem in that defects such as break-through potential frequently occur.
To reduce defects in the sapphire substrate and the nitride semiconductor thin film, a process of forming a layer of AlxGayIn1-x-yN (0≦x≦1, 0≦y≦1, 0≦x+y≦1) SiN or a laminate film with the previous layers laminated thereon, as a buffer layer, on a sapphire substrate and then growing a nitride semiconductor thin film on the buffer layer has recently been used.
If the nitride semiconductor thin film has been grown onto the buffer layer as described above, the grown nitride semiconductor thin film has break-through potential density of 108 to 109 cm−2, and thus its defect density can be reduced.
Furthermore, to manufacture a blue-violet laser diode or a high-power, high-efficiency, high-reliability light emitting diode, it is essential to reduce defect density.
To reduce break-through potential, 1) a method of forming a pattern on a sapphire substrate to adjust longitudinal and transverse growth, 2) the Lateral Epitaxial Overgrowth (LEO) method of growing a nitride semiconductor thin film onto a sapphire substrate, forming a specific shaped dielectric film on the nitride semiconductor thin film, and again growing a nitride semiconductor thin film, 3) the Pendeo epitaxial growth method of growing a nitride semiconductor thin film onto a sapphire substrate, etching the nitride semiconductor thin film into a specific shape, and again growing the nitride semiconductor thin film, and the like are generally employed.
FIGS. 1a to 1e show a process of growing a nitride semiconductor thin film using a sapphire substrate with a mask pattern formed thereon according to the prior art. Referring to the figures, a dielectric mask pattern 11 is first formed on the sapphire substrate 10 such that the sapphire substrate 10 can be exposed at a regular interval (FIG. 1a).
Then, regions of the sapphire substrate 10 that are exposed through the dielectric mask pattern 11 are etched at a predetermined depth d (FIG. 1b).
Subsequently, as shown in FIG. 1c, if the dielectric mask pattern 11 is removed, a sapphire substrate with grooves 10a formed thereon at a regular interval is finished.
Next, a buffer layer 12 is grown on an entire top surface of the sapphire substrate 10 (FIG. 1d).
Finally, a nitride semiconductor thin film 13 is grown on the top surface of the buffer layer 12 (FIG. 1e).
At this time, the break-through potential of the nitride semiconductor thin film 13A growing on side surfaces of the sapphire substrate 10 dissipates, and thus, defect density is reduced at regions of the sapphire substrate where the pattern was formed.
A method of growing a nitride semiconductor thin film using a sapphire substrate with the aforementioned mask pattern formed thereon has been recently applied to the manufacture of high-power and high-efficiency light emitting diodes.
FIGS. 2a to 2c show a process of growing a nitride semiconductor thin film by means of Lateral Epitaxial Overgrowth (LEO) according to the prior art. Referring to the figures, a first nitride semiconductor thin film 21 is formed on a sapphire substrate 20, and a dielectric mask pattern 22 is formed on the sapphire substrate 21 such that the sapphire substrate 21 can be exposed at a regular interval (FIG. 2a).
Then, a second nitride semiconductor thin film 23 is grown on regions of the first nitride semiconductor thin film 21 that are selectively exposed through the dielectric mask pattern 22 (FIG. 2b).
Here, the second nitride semiconductor thin films 23 that has been grown on the exposed regions of the first nitride semiconductor thin film 21 meet each other on the dielectric mask patterns 22 and grows further. As shown in FIG. 2c, defects in the second nitride semiconductor thin film 23 grown on the dielectric mask pattern 22 are reduced.
FIGS. 3a to 3c show a process of growing a nitride semiconductor thin film by means of Pendeo Epitaxial Growth according to the prior art. Referring to the figures, a first nitride semiconductor thin film 31 is formed on a sapphire substrate 30 (FIG. 3a). The grown first nitride semiconductor thin film 31 is etched to become a periodic stripe pattern 31a (FIG. 3b), and a second nitride semiconductor thin film 32 is laterally grown on the sapphire substrate 30 using the periodic stripe pattern 31a (FIG. 3c).
Thus, the break-through potential density of the laterally grown second nitride semiconductor thin film 32A is reduced.
As described above, according to the conventional methods of reducing defects in the nitride semiconductor, defects in the nitride semiconductor thin film that is positioned on regions where a pattern is formed or grown laterally from regions where a dielectric pattern is formed are reduced, whereas the defects remain in regions where a pattern or dielectric pattern is not formed. Therefore, there is a problem in that improvement in overall crystalline characteristics cannot be obtained.
That is, defect density is reduced as a whole, but regions where defect density is locally higher or lower exist periodically.